1. Field of the Invention
The present invention relates to a steering column system which houses a steering shaft with which tilt and telescopic operations of a steering wheel can be performed.
2. Description of the Related Art
Among automobile steering wheels, there is an automobile steering wheel which can be adjusted in upward and downward directions by the tilt operation and adjusted in frontward and backward directions by the telescopic operation so as to suit the driver's physique. The position of the steering wheel which is adjusted in the upward, downward, frontward and backward directions is fixed with a support unit configured to support a steering column housing a steering shaft toward the vehicle body (see Japanese Patent Application Laid-Open No. 2001-322552, for instance).
In this case, the support unit includes: a vehicle body-side bracket and distance pieces (connecting brackets). Here, the vehicle body-side bracket has a cross-section with an upside-down U-shape and is disposed in a way that the steering column is interposed between the two sidewall portions of the vehicle body-side bracket. The distance pieces are disposed between the inner sides of the two sidewall portions and the outer side of an outer tube. In addition, a clamp shaft (bolt) penetrates the two sidewall portions of the vehicle body-side bracket and the distance pieces. A cam part is disposed between the clamp shaft and the outer side of one of the sidewall portions of the vehicle body-side bracket. The cam part includes: a fixed cam member which is stopped from rotating by the vehicle body-side bracket; and a movable cam member which is configured to rotate integrally with an operation lever. The cam part is configured to press the two sidewall portions of the vehicle body-side bracket in such respective directions that the two sidewall portions thereof come closer to each other, or to release the two sidewall portions thereof from the press, when the clamp shaft is rotated due to the operation of the operation lever. Furthermore, the clamping is performed by pressure-contacting the two sidewall portions of the vehicle body-side bracket to the respective distance pieces when the cam part presses the two sidewall portions in such respective directions that the two sidewall portions come closer to each other.
Moreover, a looseness preventing cam configured to rotate integrally with the clamp shaft is provided between the distance pieces. When the cam part presses the two sidewall portions of the vehicle body-side bracket in response to the rotation of the clamp shaft, an eccentric cam protruding from the looseness preventing cam shifts an inner tube of the steering column to one side by pressing the inner tube from one portion (from an upper portion), and brings the inner tube into contact with the inner side of the outer tube.
In such a conventional steering column system, lower end portions of the respective distance pieces are fixed on the outer tube by welding. Here, when the two sidewall portions of the vehicle body-side bracket are pressed in such respective directions that the two sidewall portions come closer to each other, and thereby brought into pressure contact with the respective distance pieces, it is desirable that the pressure contact is achieved through their surface contact from a viewpoint of securing larger rigidity at the time of the pressure contact.
However, the lower end portions of the respective distance pieces are welded to the outer tube. Accordingly, the distance pieces and the outer tube are integrally connected together. For this reason, angles at which the respective distance pieces are attached to the outer tube are apt to change subtly due to thermal strain caused during the welding. This makes it likely that an error may occur in the dimension between an internal width between the two sidewall portions of the vehicle body-side bracket and an external width between the distance pieces.
In a case where the dimensional error occurs between the two sidewall portions of the vehicle body-side bracket and the distance pieces, when the two sidewall portions thereof are brought into pressure contacted with the distance pieces, respectively, the contact therebetween is achieved through partial contact (for instance, line contact) instead of the surface contact. This occurs due to change in a clamping force of the cam part as well. For these reasons, it is impossible to obtain stable clamped state. In addition, the contact rigidity between the vehicle body-side bracket and the distance pieces decreases. As a result, the vehicle body-side bracket and the distance pieces resonate with vibrations which are inputted through the steering channel from the road surface, the motor, and the like.
Moreover, although the eccentric cam of the looseness preventing cam brings the inner tube into pressure contact with the inner side of the outer tube by shifting the inner tube to one side when the two sidewall portions of the vehicle body-side bracket are brought into pressure contact with the respective distance pieces, this mechanism brings about the following problems. Firstly, the support strength of the pressure contact is low, and desirable stable fixing between the inner tube and the outer tube can not be obtained. Secondly, a force needed to operate the operation lever is larger since the looseness preventing cam is operated.